Best way to insulate 100 year old unfinished attic ceiling?

[Anonymous]

Rockwool? Fiberglass? Batting? Blown in? Thanks!

[Anonymous]

Insulating an attic that hasn't been insulated before, or moving where the insulating boundary is, is highly technical work. If you screw it up you can cause moisture accumulation between the roof and insulation which can lead to mold and rot and eventually the failure of the roof.

I recommend this article for a summary of the issues involved:
https://www.finehomebuilding.com/project-guides/insulation/five-cathedral-ceilings-that-work

[Anonymous]

You can totally do Rockwool yourself

[Anonymous]

Anonymous wrote:You can totally do Rockwool yourself

Rockwool directly against the underside of the roof will 100% cause moisture problems. Read the linked article. You can do it yourself and do it right, but you have to know what you're doing.

[Anonymous]

I (OP here) really appreciate the discussion. From what I saw in the article and read online, it is still very hard to know what to do.

We have an 18x10 space in a semi detached house. 100 years old. No vents. Typical DC semi detached - brick, front slope of roof covered in terracotta tile, rest of roof is flat with a 10 year old membrane on it.

We have a HVAC unit that provides AC to our upstairs located in the attic. The attic is totally unfinished with no signs of moisture. There is no insulation and two 27x38 inch windows facing south.

There is electrical for one light and the HVAC. We don't have knob and tube up there.

ALSO: When we redid our bathroom last year, the ceiling went up to the flat part of our roof where there is no crawlspace. This was loaded with old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go? Put it in the rafters, put the drywall over it and move on? Or is this a disaster?

[Anonymous]

Anonymous wrote:
We have a HVAC unit that provides AC to our upstairs located in the attic.

old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go?

First of all, having an AC unit in the attic is horrible for moisture disaster issues, though that's a whole other project and big money to fix.

So the insulation that looks like shredded paper is called "cellulose" insulation, and it is made of, wait for it, shredded paper. Very cheap and poor quality insulation, but "green" aka a scam mostly. You will spend more in utility bills from its lower rating so it is not green at all.

Cellulose insulation also is a prime mold growth medium and attracts insects, as you have found out.

Fiberglass is what you seek. Blown in is cheaper and easier to do, batting is better and more costly, doing both is best.

[Anonymous]

Anonymous wrote:

Anonymous wrote:You can totally do Rockwool yourself

Rockwool directly against the underside of the roof will 100% cause moisture problems. Read the linked article. You can do it yourself and do it right, but you have to know what you're doing.

You use baffles. Stop giving bad advice.

[Anonymous]

Anonymous wrote:I (OP here) really appreciate the discussion. From what I saw in the article and read online, it is still very hard to know what to do.

We have an 18x10 space in a semi detached house. 100 years old. No vents. Typical DC semi detached - brick, front slope of roof covered in terracotta tile, rest of roof is flat with a 10 year old membrane on it.

We have a HVAC unit that provides AC to our upstairs located in the attic. The attic is totally unfinished with no signs of moisture. There is no insulation and two 27x38 inch windows facing south.

There is electrical for one light and the HVAC. We don't have knob and tube up there.

ALSO: When we redid our bathroom last year, the ceiling went up to the flat part of our roof where there is no crawlspace. This was loaded with old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go? Put it in the rafters, put the drywall over it and move on? Or is this a disaster?

Your HVAC unit in the attic is exhausting hot air in the summer. Your attic will need to breathe. It sounds like your attic is part of the strategy to vent to the exterior. Ergo, your attic is acting as part of the exterior. If you insulate the attic roof, you are trapping the hot air in the attic, that is, hot humid air in the DC summers. I am imagining the cold ceiling surface below will be the sweat layer. Think of what a cold glass with ice does in the hot humid air - it sweats at the point of contact to that hot humid air which is the glass surface.

Why do you want to insulate the attic? To insulate the conditioned indoor air within the house?
If so, it sounds like the insulation should go on the attic floor where the conditioned indoor air is below and hot attic/exterior air above. BUT, I'm a little worried about needing a vapor barrier. Depending on your climate zone, you might need a vapor barrier.

https://buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:You can totally do Rockwool yourself

Rockwool directly against the underside of the roof will 100% cause moisture problems. Read the linked article. You can do it yourself and do it right, but you have to know what you're doing.

You use baffles. Stop giving bad advice.

What part of "directly against" didn't you read?

[Anonymous]

Anonymous wrote:

Anonymous wrote:I (OP here) really appreciate the discussion. From what I saw in the article and read online, it is still very hard to know what to do.

We have an 18x10 space in a semi detached house. 100 years old. No vents. Typical DC semi detached - brick, front slope of roof covered in terracotta tile, rest of roof is flat with a 10 year old membrane on it.

We have a HVAC unit that provides AC to our upstairs located in the attic. The attic is totally unfinished with no signs of moisture. There is no insulation and two 27x38 inch windows facing south.

There is electrical for one light and the HVAC. We don't have knob and tube up there.

ALSO: When we redid our bathroom last year, the ceiling went up to the flat part of our roof where there is no crawlspace. This was loaded with old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go? Put it in the rafters, put the drywall over it and move on? Or is this a disaster?

Your HVAC unit in the attic is exhausting hot air in the summer. Your attic will need to breathe. It sounds like your attic is part of the strategy to vent to the exterior. Ergo, your attic is acting as part of the exterior. If you insulate the attic roof, you are trapping the hot air in the attic, that is, hot humid air in the DC summers. I am imagining the cold ceiling surface below will be the sweat layer. Think of what a cold glass with ice does in the hot humid air - it sweats at the point of contact to that hot humid air which is the glass surface.

Why do you want to insulate the attic? To insulate the conditioned indoor air within the house?
If so, it sounds like the insulation should go on the attic floor where the conditioned indoor air is below and hot attic/exterior air above. BUT, I'm a little worried about needing a vapor barrier. Depending on your climate zone, you might need a vapor barrier.

https://buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation

This is gibberish. The HVAC doesn't exhaust hot air into the attic. The issue isn't heat, it's moisture. The linked article is good but it doesn't sound like you got it.

[Anonymous]

Anonymous wrote:

Anonymous wrote:
We have a HVAC unit that provides AC to our upstairs located in the attic.

old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go?

First of all, having an AC unit in the attic is horrible for moisture disaster issues, though that's a whole other project and big money to fix.

So the insulation that looks like shredded paper is called "cellulose" insulation, and it is made of, wait for it, shredded paper. Very cheap and poor quality insulation, but "green" aka a scam mostly. You will spend more in utility bills from its lower rating so it is not green at all.

Cellulose insulation also is a prime mold growth medium and attracts insects, as you have found out.

Fiberglass is what you seek. Blown in is cheaper and easier to do, batting is better and more costly, doing both is best.

Cellulose is fine. Whatever kind of insulation you have you have to manage moisture.

[Anonymous]

Anonymous wrote:I (OP here) really appreciate the discussion. From what I saw in the article and read online, it is still very hard to know what to do.

We have an 18x10 space in a semi detached house. 100 years old. No vents. Typical DC semi detached - brick, front slope of roof covered in terracotta tile, rest of roof is flat with a 10 year old membrane on it.

We have a HVAC unit that provides AC to our upstairs located in the attic. The attic is totally unfinished with no signs of moisture. There is no insulation and two 27x38 inch windows facing south.

There is electrical for one light and the HVAC. We don't have knob and tube up there.

ALSO: When we redid our bathroom last year, the ceiling went up to the flat part of our roof where there is no crawlspace. This was loaded with old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go? Put it in the rafters, put the drywall over it and move on? Or is this a disaster?

If you read the linked articles, you know that the issue is moisture management. Specifically, how to prevent moisture from inside the building from condensing when it hits a cold surface in the attic. There are two approaches, and they aren't really complementary. The traditional approach is to have ventilation between the insulation and the roof to allow moisture to dissipate. Usually the ventilated area was quite large -- the floor of the attic was insulated, and everything between the floor and the roof was ventilated. But code allows the ventilated area to be as thin as 1", so long as it is unobstructed from the eave to the peak. If you can put in a baffle from eave to peak you can put pretty much any kind of insulation below it.

The other approach is to use an insulation that is impermeable, so that moisture cannot get through to the roof. Usually this means closed cell spray foam. If your house does not have existing vents at the eaves and peak and there's no easy way to add them, this is pretty much your only option.

Having your HVAC equipment outside of the insulation, as you do now, is bad. You're essentially heating and cooling the outdoors. The equipment can get damaged by freezing as well.

[Anonymous]

Anonymous wrote:

Anonymous wrote:I (OP here) really appreciate the discussion. From what I saw in the article and read online, it is still very hard to know what to do.

We have an 18x10 space in a semi detached house. 100 years old. No vents. Typical DC semi detached - brick, front slope of roof covered in terracotta tile, rest of roof is flat with a 10 year old membrane on it.

We have a HVAC unit that provides AC to our upstairs located in the attic. The attic is totally unfinished with no signs of moisture. There is no insulation and two 27x38 inch windows facing south.

There is electrical for one light and the HVAC. We don't have knob and tube up there.

ALSO: When we redid our bathroom last year, the ceiling went up to the flat part of our roof where there is no crawlspace. This was loaded with old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go? Put it in the rafters, put the drywall over it and move on? Or is this a disaster?

Having your HVAC equipment outside of the insulation, as you do now, is bad. You're essentially heating and cooling the outdoors. The equipment can get damaged by freezing as well.

Many older houses have external packaged units containing the AC and furnace together. How would having the AC in the attic be any different that that in regards to your comments?

An AC in the attic is a poor choice obviously, due to condensation and leakage and accessibility, but curious how it would be different than a package unit with the evaporator coil outside in the box?

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:I (OP here) really appreciate the discussion. From what I saw in the article and read online, it is still very hard to know what to do.

We have an 18x10 space in a semi detached house. 100 years old. No vents. Typical DC semi detached - brick, front slope of roof covered in terracotta tile, rest of roof is flat with a 10 year old membrane on it.

We have a HVAC unit that provides AC to our upstairs located in the attic. The attic is totally unfinished with no signs of moisture. There is no insulation and two 27x38 inch windows facing south.

There is electrical for one light and the HVAC. We don't have knob and tube up there.

ALSO: When we redid our bathroom last year, the ceiling went up to the flat part of our roof where there is no crawlspace. This was loaded with old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go? Put it in the rafters, put the drywall over it and move on? Or is this a disaster?

Having your HVAC equipment outside of the insulation, as you do now, is bad. You're essentially heating and cooling the outdoors. The equipment can get damaged by freezing as well.

Many older houses have external packaged units containing the AC and furnace together. How would having the AC in the attic be any different that that in regards to your comments?

An AC in the attic is a poor choice obviously, due to condensation and leakage and accessibility, but curious how it would be different than a package unit with the evaporator coil outside in the box?

A packaged unit is going to be constructed to be outdoors. The air handler in the attic is constructed to be inside conditioned space. A ventilated attic is unconditioned space.

For most of the 20th century most people in construction thought it was OK to have basements and attics that were sorta-kinda inside the conditioned space, and sorta-kinda outside. And it was sorta-kinda OK to put mechanicals in those spaces, and if they froze in the winter you dealt with it then.

There has been a real change in the past 20 years or so in terms of what is considered acceptable (and code) in residential construction. It's now expected that there be a clear demarcation between conditioned and unconditioned spaces and that there be a continuous layer of insulation between them.

[Anonymous]

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:

Anonymous wrote:I (OP here) really appreciate the discussion. From what I saw in the article and read online, it is still very hard to know what to do.

We have an 18x10 space in a semi detached house. 100 years old. No vents. Typical DC semi detached - brick, front slope of roof covered in terracotta tile, rest of roof is flat with a 10 year old membrane on it.

We have a HVAC unit that provides AC to our upstairs located in the attic. The attic is totally unfinished with no signs of moisture. There is no insulation and two 27x38 inch windows facing south.

There is electrical for one light and the HVAC. We don't have knob and tube up there.

ALSO: When we redid our bathroom last year, the ceiling went up to the flat part of our roof where there is no crawlspace. This was loaded with old insulation that looked to be like finely shredded paper. There were a lot of moths in there and moth larvae on the exposed rafters. The contractor removed the insulation. We think it might have been original to the house as there were generally very few updates throughout.

Is blown in cellulose the way to go? Put it in the rafters, put the drywall over it and move on? Or is this a disaster?

Having your HVAC equipment outside of the insulation, as you do now, is bad. You're essentially heating and cooling the outdoors. The equipment can get damaged by freezing as well.

Many older houses have external packaged units containing the AC and furnace together. How would having the AC in the attic be any different that that in regards to your comments?

An AC in the attic is a poor choice obviously, due to condensation and leakage and accessibility, but curious how it would be different than a package unit with the evaporator coil outside in the box?

A packaged unit is going to be constructed to be outdoors. The air handler in the attic is constructed to be inside conditioned space. A ventilated attic is unconditioned space.

For most of the 20th century most people in construction thought it was OK to have basements and attics that were sorta-kinda inside the conditioned space, and sorta-kinda outside. And it was sorta-kinda OK to put mechanicals in those spaces, and if they froze in the winter you dealt with it then.

There has been a real change in the past 20 years or so in terms of what is considered acceptable (and code) in residential construction. It's now expected that there be a clear demarcation between conditioned and unconditioned spaces and that there be a continuous layer of insulation between them.

Thanks for the response. So outdoor package units are insulated around the evap coil I'm assuming then?